When using Sableye's "Junk Hunt" attack, do I have to show my opponent which 2 Item cards I put from my discard pile into my hand?
Yes, you do. The Discard Pile is a public zone, and you can't do anything to it that your opponent isn't fully aware of.
Source: TPCi Rules Team (2012-08-23)

Relevant cards

Note: All applicable cards may not be listed below.
BW5_62